1. Technical Field
This invention relates in general to cooling systems for electrical component enclosures, and in particular to an improved valve for an electrical component enclosure cooling fan.
2. Background Art
Electronic cooling systems designed for high availability or continuous operation often employ redundant fans that are arranged in parallel. This arrangement is used to guard against catastrophic loss of cooling flow in the event of a single fan device failure. One problem with this type of parallel fan configuration is that when one fan fails, the pressure difference across the surviving fan pushes air backwards through the failed fan. This reduces the delivered flow rate that would otherwise be available from the surviving fan by almost half
To prevent back flow, the normal practice is to add a flap-type device on the exhaust side of the fans. Common flapper designs include swinging door flaps and multiple slat vanes. However, prior art designs neglect the inherent helical or swirling discharge pattern of tube axial exhaust fans, thereby inadvertently producing large pressure drops during normal operation of the fan before failure. It is well known tube axial fans have a discharge angle that is a direct function of the static pressure operating point on its pressure-flow curve. There is always some angle or spiral to the axial discharge direction. Indeed, the development of pressure in tube axial fans is dependent on the change in momentum brought about by changing the direction of the air. The spiral is never absent, even at free-air delivery, as velocity pressure must still be produced. The spiral always rotates in the same direction as the fan blade and appears as a helical vortex in flow visualizations. In addition, prior art designs tend to take up significant amounts of space in the axial direction that make parallel fan configurations difficult to implement in compact packages. Thus, an efficient, axially compact design for high availability exhaust fans is needed.